Although I have never used MultiBit HD but only the classic version, from what I read the file you have (mbhd.wallet.aes) should be quite enough to get your seed from it. What matters is that the file is not encrypted with seed words which would be the case if you had a file called multiBit.zip.aes file.
What you need is one, as they say, a fairly simple tool that you can find here :
https://github.com/gurnec/decrypt_bitcoinj_seedRead all warnings and instructions carefully, and also pay attention that you have a clean OS (no virus/malware) that could steal the seed - of course I recommend that you be offline during the process.
If you manage to get your seed, the next logical step would be to enter it in a desktop wallet - Electrum is free and quite popular, just beware of fake versions and download it only from
https://electrum.org/#homeTo restore your seed in Electrum follow this instruction :
https://bitcoinelectrum.com/restoring-your-multibithd-wallet-in-electrum/
